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 Tire Size & Speedometer Correction - Evidence
I'll admit to an odd quirk I live with. That is that when I look at my speedometer, I'd like for it to tell me how fast I am going, not within 3-4 mph of how fast I am going. When I bought and installed my replacement rear tire (Michelin HydroEdge 215/60R15), I found my speedometer error rate dropped significantly. Now my speedometer reads either the same or within 1 mph of my Garmin Zumo 550 GPS. See the picture below for proof. This is typical of any speed I have checked. I've run this tire for over 11,000 miles and have had no Nanny issues associated with it. I have worn through 1/3 of the legal tread, so expect to get another 22,000-23,000 miles out of it before changing. Picture was taken last Monday night on the way home from Bible study.
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I got exactly the same speed results with a 205-60-15 General and now with the Pirelli P4.
Two Wheelers from 1963-2011
Three Wheelers:
2011 RT(Red)
2014 RT(white)
2016 F3T(red)
2022 RT current ride(silver)
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2016 Slingshot
2018 Vanderhall
2019 Slingshot
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Let's see..!!
if you want accurate use your gps. Not even from the factory are the spot on. Highway speed signs always differ so gps is best. Different tires can make a difference but then not that much....
2012 RS sm5 , 998cc V-Twin 106hp DIY brake and park brake Classic Black
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What air pressure do you run in that Michelin ?
2016 F3 Limited
2019 Ryker Rally
2014 Suzuki V Strom 650
2020 CSC TT 250
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 Originally Posted by Highwayman2013
What air pressure do you run in that Michelin ?
I'm running the BRP recommended pressure, around 28 psi. After 11,000+ miles, I ran a tread depth gauge across the tire and found that the tread depth is even across the width of the tire, so I'm satisfied. I also have the Michelin Defenders on the front (175/65R14) & am running around 18-20 psi in them. I don't have that many miles on them yet, but initial indicators are that they're wearing evenly and should last 50,000 miles or more.
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Have you got a picture of the rear tire, the correct tire is a 225/50R so I was wondering what the 60 looks like and how it fits the Rim.
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Very Active Member
Originally Posted by bluestratos
Have you got a picture of the rear tire, the correct tire is a 225/50R so I was wondering what the 60 looks like and how it fits the Rim.
Hmm, I have noticed my speed is off as well compared to my Garmin 660 (as much as 4mph in some cases), just replaced mine with the 225/50 Khumo or I would have tried a 60 as well.
PS. You need to drive faster, old man!!
PSS. You need gas!!!
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You can't go wrong with gps reference., thanks also with the tires and pres info.
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Tire Size Specs
Thanks for the great post about speedo accuracy Mark, great info! 
There are many of use who run 4-ply automotive tires on our Spyders. In the stock 225/50R15 rear tire size there are limited options, this is why many have tried other sizes to open up the options of what is available. As a side benefit, the speedo becomes more accurate, as Mark has shown us.
In regards to this, here are some of the other sizes and how they differ in diameter. The first number (225, 215, 205) is the tire width in mm, so going to a 215 instead of a 225 width you are going 10mm narrower (which is 0.39"). Going to a 205 is 20mm narrower (0.79").
Diameter is not as clear cut. The stock 225/50R15 tire is 23.86" in diameter (or 606mm). When you go to a 215/60R15 it is 25.16" (639mm) in diameter, or +5.4% larger. Another popular size with many options is 205/60R15 and this one is even closer in diameter to the stock tire at 24.69" diameter (627mm) which is only +3.5%, but is slightly narrower in width. Both of these sizes have been used by forum members with good success. The nanny does not care about this size difference.
There are some other sizes, but very few tires are available in these. Like 215/55R15 (+1.9%) or 205/55R15 (+0.1%) sizes, they are closer in diameter to the stock tire than the 60s. There’s also 225/55R15 but this too is tough to find, that one is +3.7% in diameter.
Here is a great link to a tire size calculator I use to figure all of this out - http://www.tacomaworld.com/forum/tirecalc.php
The 4-ply tires seem to be slightly heavier, but this is perfectly acceptable for the higher quality and durability. I have been using 4-ply tires for years on Spyder for their more even wear and greater durability. Just pay attention to their speed ratings, tread wear rating, traction and temperature ratings. Personally, I will only use a tire that is AA or A for traction, only A for temperature, and H (130 mph) or V (149 mph) for speed rating (I will not use a T rated tire, that is only 118 mph). Hope this helps!
2021 RT Limited - Deep Marsala Red – 4,200 miles
2013 ST-S SE-5 - Circuit Yellow – 56,000 miles
2015 F3-S SM-6 - Can-Am Red Solid Gloss – 2,000 miles - SOLD
2008 GS SM-5 Premier Edition #659 - Full Moon – 34,000 miles - SOLD
2008 GS SM-5 Premier Edition #006 - Full Moon – 34,800 miles - SOLD
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Last edited by MarkLawson; 10-31-2013 at 01:19 PM.
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www.TireRack.com says they have 'fewer than 3' in stock ( http://www.tirerack.com/tires/TireSe...60&diameter=15 ) @ $108.00 each (Closeout) + shipping. I understand their Defender is the replacement for the HydroEdge.
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Excellent Rain Tire Too
That's another thing about car tires, specifically how they perform in rain. Hydroplaning is the last thing you'd want. I changed aspect ratio on the rear tire of that Triumph Rocket III and the circumference was something like 2 percent smaller on the longer lasting Michelin I went to. That made the odometer register 100 miles when I had only covered 98. That doesn't sound like much until you multiply the odometer error. 1000 miles only being 980 or 10,000 being 9,800 miles etc. My guess if you're car tire gets you closer or dead-on with your GPS there should be zero or near zero odometer error as well.
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Tire Rack.com has a few left. I just bought one on Saturday for 108.00 plus shipping. Ordered it Saturday and it was delivered on Tuesday. Can't wait to have it installed to see how it rides, I have 12,200 miles on my Kendall, center is worn into the wear strips. Russ
Last edited by xmanjr; 11-22-2013 at 07:39 PM.
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Only 2 Michelin HydroEdge remaining. I order one 5 minutes ago.
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Another picture @ another speed taken this past Sunday:
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Very Active Member
215/60R15
215/60R15.....????
you should be riding on a 225/50 R15.... the '50' vs. '60' is what's skru'n u up....
the 225 vs. 215 is the width.... no issues there, except you don't have as much 'rubber' on the ground...
'50' vs. '60' is the diameter of the tire... that makes all the different in speedo numbers... as well as MPG...
burn the BAD-BOY up, and get u a 225/50 R15 ASAP.....
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Hi all with the tyre being a little bigger in diameter how much harder is it to take off with the trailer attached because I have a 2010 rt manual and have already replaced a clutch because 1st gear is so tall.
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Originally Posted by SPYD3R
215/60R15.....????
you should be riding on a 225/50 R15.... the '50' vs. '60' is what's skru'n u up....
the 225 vs. 215 is the width.... no issues there, except you don't have as much 'rubber' on the ground...
'50' vs. '60' is the diameter of the tire... that makes all the different in speedo numbers... as well as MPG...
burn the BAD-BOY up, and get u a 225/50 R15 ASAP.....
Actually, the statement about 'rubber on the ground' is incorrect. On the same vehicle at the same inflation pressure, all tires put the same amount (area) of rubber on the ground. 500 pounds setting on a tire inflated to 28 psi will generate a contact patch of 27.14 sq in, regardless of whether the tire is 250 mm wide or 180 mm wide. The difference will be the way the contact patch is aligned relative to the direction of travel. The tire with the greater width will have a contact patch which is wider and shorter than the narrower tire.
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Very Active Member
I DON'T THINK SO
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Originally Posted by SPYD3R
215/60R15.....????
you should be riding on a 225/50 R15.... the '50' vs. '60' is what's skru'n u up....
the 225 vs. 215 is the width.... no issues there, except you don't have as much 'rubber' on the ground...
'50' vs. '60' is the diameter of the tire... that makes all the different in speedo numbers... as well as MPG...
burn the BAD-BOY up, and get u a 225/50 R15 ASAP.....
I don't think you're understanding the point of my post. With the different tire installed, my speedometer is now running true, for the most part. At some speeds it shows 1 mph different. Overall, I think this is a good change. I cannot speak to contact patch sizes, but the change in width is minimal. I have not found this tire to present any perceivable change in traction.
Originally Posted by BLUEKNIGHT911
Dan I beg to differ on this .......50 vs. 60 is the aspect (?) ratio ....it has nothing to do with the tire diameter...Mike
Actually, as I understand it, the aspect ratio measurement is based on the tread diameter. A '50' means the side height is 50% of the tread width. On a 225/50R15, that would mean the sidewall height is 112.5mm. For a 215/60R15, the sidewall height would be 129mm, resulting in a 'taller' tire than OEM.
Someone please correct me if I am wrong, which is always a good possibility...
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Right. And the difference between 50% and 60% is small. Best thing is the speedometer is running true.
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) quite awhile ago, .......but you may still find some hidden away....Mike 
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